1. Field of the Invention
The present invention is directed to constructions for expansion joints for ducting, for example, such as may be used for the exhaust for large stationary gas turbines for the generation of electrical power, and for other ducting environments, especially those involving high temperature and/or substantial flow pulsations or turbulent flow.
2. Prior Art
Ducting which is used to transport air or other gaseous flows that are subject to substantial pulsations or turbulent flow or wide variations in pressure or flow rate, or which has wide variations in temperature range, typically must be provided with expansion joints that will enable the ducting to expand or contract to accommodate such dimensional variations as may be caused by extremes of pressure or temperature variation. In addition, if the ducting is connected to a air or other gaseous flow source that is pulsating, vibrating or in some other form of movement, expansion joints are also necessary in order to accommodate such dimensional changes or movements, without transmitting the stresses, vibrations or movements along the ducting. Otherwise, the ducting might be subject to leakage or failure entirely.
One example of an environment in which such ducting is necessary is that of a stationary gas turbine that is used for electrical power generation. Expansion joints for ducting for gas turbines must be able to accommodate relative axial movements of the duct ends on opposite side of the joint, as well as relative vertical and/or horizontal movements of the duct ends.
A joint for use with ducting such as used in association with such moving air or other gaseous flow sources is typically formed by creating a gap in the ducting (which ducting typically may be round or rectangular in cross-section). Inner and outer liner duct structures are then affixed to the opposing duct ends. The inner and outer liner duct structures are in overlapping telescopic relation to one another, with the inner liner duct structures on the upstream side of the joint. In this way, the force of the gas flow, during ordinary operating conditions, has less of a tendency to drive the gases between the overlapping portions of the inner and outer liner duct structures. A relatively close fit between the overlapping portions is provided, so that the impact of high-magnitude pulsations or turbulent flow in the air or other gaseous fluid flow, on the remaining surrounding expansion joint structure, is reduced.
Because of the need for longitudinal and vertical movement accommodation, the expansion joint may or may not be a monolithically formed structure that is uniformly constructed around its periphery. The inner and outer liner duct structures on the top and bottom of the expansion joint may overlap one another in regions extending across the width of the joint, and relative movement of the inner and outer duct liner structures is in the longitudinal direction. In addition, the junction of the liner duct structure, at one end of the joint, is provided with a vertical slip feature, that permits one end of the joint to move, for example, several inches up or down, relative to the other end, without creating any gaps that would permit pulsations or turbulent flow of the air or other gaseous flow to affect the remaining surrounding expansion joint structure.
To the outside of the liner duct structure, a plurality of insulating pillows is arranged, so as to further prevent leakage of the exhaust gases through the joint, and to prevent heat loss through the joint. Typically, several layers of insulating pillows are used.
Finally, a high-temperature flexible belt is provided to create the flexible outer skin of the expansion joint, connecting the portions of the duct on opposite sides of the gap.
Such a construction is generally effective in providing accommodation for vibratory or other movements, as well as dimensional changes imposed by thermal or pressure variations in the operating regime of the duct. However, because the inner and outer liner duct structures must have some clearance, in order to permit relative movement, of necessity gases will infiltrate the passages between the liner structures. As these gases are often very high temperature and/or corrosive, they can contribute to the degradation of the insulation pillows.
Accordingly, it would be desirable to provide a means for reducing degradation of insulation pillows in such expansion joints, by providing increased protection of the insulation pillows, and reduced likelihood of effect on the insulation pillows arising from pulsations and/or turbulence in the air or other gaseous flow.
This and other desirable characteristics of the present invention will become apparent in view of the present specification, including claims, and drawings.
The present invention is directed to an expansion joint for flexibly connecting first and second duct ends. The expansion joint has a longitudinal axis, and a periphery.
The expansion joint comprises an inner liner duct structure, operably affixed to and extending substantially longitudinally from the first duct end toward the second duct end. The inner liner duct structure extends substantially along the inner periphery of the first duct end. An outer liner duct structure is operably affixed to and extending substantially longitudinally from the second duct end toward the first duct end. The outer liner duct structure extends substantially along the inner periphery of the second duct end. The inner liner duct structure at least partially longitudinally overlaps the outer liner duct structure. The inner and outer liner duct structures define a flow path through the expansion joint.
At least one insulation pillow member is operably positioned substantially outside of the inner and outer liner duct structures, relative to the flow path. The at least one insulation pillow is further operably disposed between the first and second duct ends for providing pulsation damping between the first and second duct ends, and/or for providing thermal insulation for retarding the migration of heat from the expansion joint.
A flexible sealing cover peripherally surrounds the at least one insulation pillow member, and substantially sealingly connecting the first duct end to the second duct end.
A bellows liner structure is operably disposed between the inner and outer liner duct structures, and is oriented to the inside of the at least one insulation pillow member. The bellows liner structure is engaged in a compressive, substantially sealing relationship, relative to the inner and outer liner duct structures, for substantially precluding exposure of the at least one insulation pillow member to air or other gaseous from the flow path that can infiltrate past the overlapping inner and outer liner duct structures.
Preferably, the bellows liner structure comprises at least one distinct bellows liner member disposed about at least a portion of the periphery of the expansion joint, between the inner and outer liner duct structures, and the at least one insulation pillow member.
In a preferred embodiment of the invention, at least one distinct bellows liner member is disposed along a bottom side of the expansion joint, and affixed at at least one end thereof, to one of the inner and outer liner duct structures. In an embodiment of the invention, at least one distinct bellow liner member may have one end that is free to slide relative to one of the inner and outer liner duct members, when the expansion joint undergoes axial dimensional changes.
Preferably, the at least one insulation pillow member comprises an inner insulation layer; an intermediate layer; and an outer covering. The inner insulation layer is preferably fabricated from at least one insulating material selected from the group consisting of: fiberglass; ceramic mat, wire screen or mesh, woven fiberglass or ceramic blankets. The intermediate layer is preferably fabricated from metal mesh material. The outer covering is preferably fabricated from a metal coated layer of woven fabric material. The woven fabric material is preferably fiberglass.
The flexible sealing cover may comprise an innermost layer of fiberglass fabric; a layer of film made of polytetrafluoroethylene (PTFE) sometimes sold under the registered mark Teflon(copyright); a layer of metal loop mesh; and an outer layer of metal coated fiberglass.